Effect of Avoparcin on the ruminal degradability of nutrients

The aim of this experiment was to investigate the impact of the glycopeptide compound, Avoparcin, on the growth-promoting effect in ruminal fermentation and nutrient degradability of ruminants. The effect of Avoparcin was studied as a function of concentrate to forage ratio of the diet in wethers provided with rumen and duodenal cannulas. Two control (I. and II.) groups were formed where the concentrate to forage ratio was changed from 70:30 (group I.) to 30:70 (group II.). In the self-control experiment the feeding of control diets was followed by the administration of experimental diets containing Avoparcin (groups I.+ A. and II.+ A.). Irrespective of concentrate to forage ratio, Avoparcin reduced the molar percentage of acetic acid and increased that of propionic acid, the acetic acid/propionic acid ratio decreased and the molar proportion of isobutyric acid increased. Ammonia concentration in the rumen fluid was significantly lower in group I.+ A. than in the corresponding control group (I.). Avoparcin supplementation of diet II. improved the apparent digestibility of organic matter from 52.9 to 56.4. Avoparcin in the diet of high proportion concentrate decreased the true digestibility of organic matter from 77.0 to 72.5. Avoparcin significantly increased the ruminal degradation of cellulose and hemicellulose in group II.+ A. Avoparcin supplementation of the diets had no effect on the duodenal flow of total N and non-ammonia-N, however the microbial N content of the duodenal chymus was significantly lower irrespective of concentrate to forage ratio. At the same time in group I.+ A., the amount of dietary N passed from the rumen into the duodenum in 24h was significantly higher (7.1 g/day vs. 2.7 g/day). Avoparcin supplementation of the high forage ratio diet (II.) increased the apparent digestibility of N in the rumen. In contrast, in wethers fed a diet of high concentrate ratio (I.), the true ruminal digestibility of N-compounds decreased. Irrespective of concentrate to forage ratio of the diet, the efficiency of microbial protein synthesis was reduced by Avoparcin. The experimental results (enhanced propionic fermentation and the higher ratio of undergraded bypass protein reaching the duodenum) support the observation that Avoparcin increases the body weight gain of fattening animals